The present invention relates to an apparatus for collecting chemical samples, and more specifically, to an apparatus that is capable of collecting particles or molecules adhered to a surface.
Many situations arise requiring the capability to detect the presence or absence of a chemical on a surface. One important example is the detection of toxic and hazardous substances in the environment, such as explosives and chemical agents. Searching for toxic or hazardous substances involves monitoring a variety of different surfaces and checking for the presence of particular chemicals.
In general, the process of detecting a chemical comprises three main steps: acquiring the sample, conditioning the sample, and employing a chemical detector to detect, identify and quantify the specific chemical of interest, herein referred to as the target analyte or target. Sample acquisition comprises the removal of the target analyte from a surface or host matrix to which it may be attached. Sample conditioning comprises the preparation, conditioning, or processing of the sample prior to its introduction to a chemical detector. Detecting the target analyte with the chemical detector involves determining the presence or absence of the target chemical on or in the chemical detector.
Although chemical detection is conventionally viewed as being defined by the lower limit of the detection ability of the chemical detector, the performance of the chemical detector alone does not accurately characterize the ability of the entire system to detect the presence of a specific chemical. In many cases, performance is significantly affected by sample acquisition and conditioning.
Often, it is difficult to acquire a chemical sample when the chemical is adhered to a surface, particularly if the vapor pressure of the chemical is low, or if the temperature is low. Under these circumstances, only a small amount of molecules may be in the gas phase and available for collection. Additionally, the surface of the chemical may become crusted-over with time, which further reduces the quantity of vapors in the gas phase available for detection.
Accordingly, a need exists for an improved system for collecting chemical samples, particularly when the chemical is adhered to a surface.
The present invention comprises an apparatus for collecting particles, such as molecules, that are adhered to a surface. The apparatus comprises an outlet that ejects fluid for dislodging the particles from the surface and an inlet for collecting the particles once dislodged. The particles may, for example, be in the form of an aerosol or vapor.
In the preferred embodiment, the fluid is warm air and a plurality of outlets are employed to eject pulses of the warm air. A blower draws air from the atmosphere and supplies that air to the outlets to dislodge or desorb the particles while a pump provides suction to draw the particles into a plurality of inlets. Intermittent flow of air through the outlets may be achieved by means of a valve, or alternatively, by blower control electronics that switch the blower on and off. Intermittent suction at the inlets may be provided by activating the pump intermittently or, alternatively, by using a valve.
According to another aspect of the invention, a method for collecting particles, such as molecules, that are adhered to a surface comprises ejecting fluid onto the surface to desorb the particles from the surface and drawing the desorbed particles into an inlet. The particles can then be detected using a chemical detector. In the preferred embodiment, the ejected fluid comprises pulses of air which are diverted against the surface and the drawing is accomplished using intermittent suction. Such ejection may be alternated with the drawing. In another embodiment, continuous suction is provided throughout a plurality of blowing periods. In the preferred embodiment, the fluid as well as the desorbed particles are heated. For example, the desorbed particles may be heated by heating the inlet. Preferably, the fluid directs the desorbed particles toward the inlet.